一個簡單的Android軌跡動畫

public class TestView extends View implements ViewTreeObserver.OnGlobalLayoutListener{
 private Paint paint = new Paint();
 private Bitmap bitmap;
 private int[]local;
 boolean enter = false;
 int count;
 ViewTreeObserver observer;
 Canvas canvas;
 float lastX = 0;
 float lastY = 0;
 
 public TestView(Context context) {
  super(context);
 }
 
 public TestView(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  observer = this.getViewTreeObserver();
  observer.addOnGlobalLayoutListener(this);
  getImageFromAssetsFile("target.png");//讀取圖片
 }
 
 public TestView(Context context, AttributeSet attrs) {
  super(context, attrs);
  observer = this.getViewTreeObserver();
  observer.addOnGlobalLayoutListener(this);
  getImageFromAssetsFile("target.png");
 }
 
 private void getImageFromAssetsFile(String fileName) {
  AssetManager am = getResources().getAssets();
  try {
   InputStream is = am.open(fileName);
   bitmap = BitmapFactory.decodeStream(is);
   is.close();
  }
  catch (IOException e) {
   e.printStackTrace();
  }
 }
 
 
 private void filterColor(){
  int w = bitmap.getWidth();
  int h = bitmap.getHeight();
  int[]pixels = new int[w*h];
  local = new int[w];//以原圖寬為單位，保存點在原圖Y軸上的位置
  bitmap.getPixels(pixels,0,bitmap.getWidth(),0,0,bitmap.getWidth(),bitmap.getHeight());
  for(int i = 0; i < w; i++){
   int lenght = 0;
   int total = 0;
   for(int j = 0;j<h;j++){
     if (bitmap.getPixel(i, j) !=0) {
      lenght++;
      total+=j;
     }
   }
 
   System.out.println(lenght+"");
   if(lenght<15||((float)i/(float) w)<0.85)
    local[i] = total/lenght;
   else
     break;
  }
 }
 
 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  if(enter) {
   paint.setAntiAlias(true);      //設(shè)置畫筆為無鋸齒
   paint.setColor(Color.WHITE);     //設(shè)置畫筆顏色
   canvas.drawColor(Color.TRANSPARENT);     //透明背景
   paint.setStrokeWidth((float) 6.0);    //線寬
   paint.setStyle(Paint.Style.STROKE);
 
   Path path = new Path();
   path.moveTo(0, (((float) getMeasuredHeight()-25) / (float)bitmap.getHeight()) * (float) local[0]+7);
   if (count <= bitmap.getWidth()) {
    if(count<bitmap.getWidth())
     count++;
    for (int i = 1; i < count - 1; i++) {
     if(local[i]>0) {
      path.lineTo((getMeasuredWidth() / (float) bitmap.getWidth()) * (float) i, (((float) getMeasuredHeight()-25) / (float) bitmap.getHeight()) * (float) local[i]+7);
      lastX = (getMeasuredWidth() / (float) bitmap.getWidth()) * (float) i;
      lastY = (((float) getMeasuredHeight()-25 )/ (float) bitmap.getHeight()) * (float) local[i];
     }
    }
   }
   if(count<bitmap.getWidth())
    postInvalidate();
   else {
    count = 0;
    postInvalidate();
   }
    canvas.drawPath(path, paint);
    paint.setStyle(Paint.Style.FILL);
    canvas.drawCircle(lastX, lastY+7, 7, paint);
//   }
  }else{
   this.canvas = canvas;
  }
 }
 
 @Override
 public void onGlobalLayout() {
  filterColor();
  enter = true;
  postInvalidate();
 }
}